Arylamines are of considerable importance in a variety of industries. As such, the development of new and more general methods for their preparation is of significant interest. There is ample literature available on preparation of arylamines under catalytic conditions. The catalysts normally used in the synthesis are transition metal catalysts like Tin, Palladium and Copper.
Establishing an efficient, reliable method for the N-arylation of amines is currently a very active area of research in organic synthesis. Such aryl subunits are commonly found in a variety of biologically active and natural compounds, agrochemicals, HIV-protease inhibitors, and also compounds of interest in material science. Traditionally, the N-arylation of amines has been carried out under copper-mediated Ullmann-type conditions involving the coupling of amines with aryl halides. Although these copper-promoted reactions are useful, they usually require harsh reaction conditions and stoichiometric amounts of copper, and the yields are not very reproducible.
Article titled, “Palladium-Catalyzed Synthesis of Arylamines from Aryl Halides. Mechanistic Studies Lead to Coupling in the Absence of Tin Reagents” by Janis Louie and John F. Hartwig in Tetrahedron Letters, 1995, Vol. 36, No. 21, pp. 3609-3612 reports a reaction of aryl halides with secondary amines in the presence of silylamide base and tri-o-tolyphopshine palladium complexes to give arylamine products. This process provides a convenient method for performing this heterocross coupling reactions without the necessity for forming tin amides and disposing of tin halides. Further, it reports that this reaction follows from a mechanistic analysis of the coupling reaction with tin amides and occurs as a result of the cleavage of palladium aryl halide dimers with secondary amines.
Article titled, “A Simple Catalytic Method for the Conversion of Aryl Bromides to Arylamines” by Anil S. Guram, Roger A. Rennels, and Stephen L. Buchwald in Angew. Chem. Int. Ed. Engl. 1995, 34. Issue No. 12 reports a facile and general catalytic method for the conversion of aryl bromides to arylamines, which works well for inter- and intramolecular processes. Further, it reports that this method include the experimental simplicity with tin/boron-free conditions, and has a broad substrate scope.
Article titled, “Nickel-catalyzed amination of aryl carbamates and sequential site-selective cross-couplings” by Tehetena Mesganaw, Amanda L. Silberstein, Stephen D. Ramgren, Noah F. Fine Nathel, Xin Hong, Peng Liu and Neil K. Garg in Chem. Sci., 2011, 2, 1766 reports the amination of aryl carbamates using nickel-catalysis. It also demonstrates that aryl carbamates are outstanding precursors for the synthesis of polysubstituted aryl amines using sequential carbamate functionalization/site-selective coupling processes.
Recent developments in transition-metal-free carbon-carbon and carbon-heteroatom bond-forming reactions utilizing a versatile class of reactive intermediates, viz., arynes, holds the potential for numerous applications in organic synthesis. Consequently, arynes have been employed for the construction of multisubstituted arenes with structural diversity and complexity. The versatile transition-metal-free applications of arynes include cycloaddition reactions, insertion reactions and multicomponent reactions. In addition, arynes have found applications in natural product synthesis.
Article titled, “Transition-metal-free α-Arylation of β-keto amides via an interrupted insertion reaction of arynes” by Kishor Mohanan, Yoann Coquerel, and Jean Rodriguez reported in Org. Lett., 2012, 14 (17), pp 4686-4689 reports direct α-arylation reactions of secondary β-keto amides with arynes, generated by fluoride-induced elimination of ortho-silylaryltriflates. The transformation proceeds via an interrupted insertion reaction of arynes and leads to densely functionalized aromatic compounds exhibiting a chiral ‘all carbon’ quaternary center under transition-metal-free conditions.
There are several reports on transition-metal-catalyzed, synthesis of tertiary aryl amine derivatives, but the transition-metal free syntheses of tertiary arylamine derivatives are relatively rare. For example, a facile synthesis transition-metal-free procedure for the N-arylation of amines by Zhijian Liu et al reported in J. Org. Chem. 2006 Apr. 14; 71(8): 3198-3209 reports a reaction of amine with variety of o-silylaryl triflates in the presence of CsF in acetonitrile to yield the N-arylated amines. However, in the inventor's hands, synthesis of aryl amines were achieved using primary and secondary amines only, but using tert-amines, the arylation was not feasible. Despite these significant recent improvements, there still remains a need in the art to prepare tertiary arylamine derivatives in good yields utilizing the cheaper sources in cost effective manner.